A bunch of obligations that two people have for each other that make both of them feel worse about themselves.

To quote the majority of the song "Piss Off" by the Arrogant Sons of Bitches (A break-up song):

"P-I-S-S-O-F-F-Hey!

I remember way back when,
When I wanted you to be mine.
And now that I've kind of had you,
I wonder was it all just a waste of time?
And did it make sense jumping into something
Knowing that I'd get hurt?
I don't know, but my boss thinks not,
It makes me less productive at work!

And all my friends told me "look out!"
'Cause you were treating me like shit!
I swallowed my pride and bit my tongue,
And I thought nothing of it!
I blame relationship's termination
For why things are never fine.
I've dreaded this moment from the day we met:
We have to say goodbye!

Now all I do is pine and smoke
With all my friend.
I regret not moving on
Even though I said I did,
Fuck, shit, dammit.
How many times do I have to call you
Just because you call me first?
You see, we're nothing together
But a bunch of obligations
That just make me feel worse!

So why was I the last to know
When you ride some other guy?
And why should I have even cared
That night you said you cried?
My stomach threw up my daily nutrition
And your anti-morals robbed me blind.
I loved you, and you blew it,
And you broke your own heart.
So eat this last goodbye!

The most un-sturdy and uncertain vessel to navigate through any ocean of the heart. While the warm winds of prevailing love and romance blow favorably through its sails, this un-seaworthy vessel steers ahead with pride and promise. But upon hitting rough and stormy weather, too often the relationSHIP flounders and sinks.

If you've yet to experience a relationship, then an example will do little to help you understand.